To reduce the burden on the environment of the synthetic resin waste, biodegradable resins, such as polylactic acid resin or the like, that can be decomposed by bacteria or other microorganisms in the soil or the like after disposal have recently been proposed.
There has been known a conventional method for producing a food container used as a cup, a bowl, a tray, or the like by injection molding of a polylactic acid resin (see Patent Literature 1, for example).
According to the above-described production method, the food container is formed by injecting a molten resin of a polylactic acid into a cavity defined by a female mold and a male mold opposed to the female mold, the female mold having a recess shaped to conform to the outer shape of the food container, and the male mold having a projection shaped to conform to the inner shape of the food container. The cavity provides a gap corresponding to the thickness of the food container between the recess and the projection. The above-described method can produce a thick container having a thickness of about 2.5 mm by injection molding. However, in the fields of the food containers, the single-use containers for medical purposes, powder storage containers and the like, production methods are desired to be capable of forming a thinner container having a thickness of about 0.7 mm, for example.